Also to remind you that you need to study all the materials covered in lectures and also those in the mind maps, ppts, and notes. Only the topics covered in lectures will be included in the final examination. For example, if I do not cover fungal pathogens in the lectures then fungal pathogens will not be inlcuded in the final examination.

The final examination will carry two parts, 50% each. One part from Professor Chung and one part from me.

Go to the FNSC5110 blog to see the questions asked by the students in previous years and also the answers.

I am reviewing the old paper about FNSC4180/FNSC3180 and I found that the exam paper covered some questions about HACCP and hazard analysis. Will this part of content also be included in FNSC 5110 final exam? I remember that you did not cover this part of the content in our lecture.

Monday, November 28, 2016

I think you
have look at the old exam paper of FNSC3180/4180. Question B3 has not been
covered in FNSC5110 lectures this year and not in past few years so it will not
be included in the final examination.

The other
question is straightforward:

B3a What are the numbers of D'S targeted in the standard
canning process for each of these microorganisms? (3 marks)

Number of D= anti-log10(Starting density/acceptable density)

For example: spoilage bacteria

Number of D = anti-log10(100/0.00000001) = anti-log10 of
10^10 = 10

Answer is 10D

Sorry, my answer is wrong: The targeted number of D's in the standard canning process should be:25/0.25 = 100DBecause I missed the part of the question of "standard canning process", which means the condition is set as the process. So the achieved number of D's should be the answer.

li.
Lunch in the picnic was served at 12:00 noon on Saturday. Dinner was finished
by 7:00pm that evening.

iii.Patients started to have diarrhea at 1 1 :00pm on Saturday followed by
severe vomiting. Some of them went to the hospital immediately after they were
sick. The last patient felt sick and went to the hospital at 4:00am on Sunday.

v.The laboratory of the Health Department detected low levels of
Salmonella enterica serotype Typhimurium from sushi left over from the picnic
and refrigerated after lunch. Also detected are low levels of Staphylococcus
aureus from the dough used to make the pizzas and Low levels of Clostridium
perfringens endospores in the vegetable stock used to make the turkey stuffing.
No bacteria or spores were found from bread, fried noodles, boiled chicken, or
fried rice.

vi.The turkey and bread were prepared in the morning and transported to the
picnic area at room temperature. The sushi was also made in the morning, stored
in a foam box with ice and transported to the picnic area. The pizzas were baked
right before lunch time and transported to the picnic area and they were kept
at 65-70 0 C. Boiled chickens were cooked the day before the picnic
and kept in refrigerator and sent to the picnic without refrigeration. Fried
rice and fried noodles were prepared at noon and transported to the picnic area
in containers kept at 65-70 0 C by the supplier.

vii.Most of the patients recovered after one day of rest.

a.The
foods consumed at breakfast and lunch and the illness records are listed in the
following table, calculate the attack rates. Which food would be the most
suspected food? Explain briefly. (8 marks)

Foods served

Ate

Did not Eat

well

111

Total

Attack rate

Well

111

Total

Attack rate

Pizza

68

40

108

47

5

52

Sushi

66

15

81

49

30

79

Bread

96

40

136

19

5

Boiled Chicken

70

32

102

40

18

58

Roast turkey

64

35

99

51

10

61

Fried rice

50

17

67

63

30

93

Fried
noodles

75

25

100

42

18

60

B5.
You are the senior technical manager of a well-known ham canning factory.

One
day the technician rushed into your office and informed you that the ham
delivered yesterday for canning was slightly contaminated in an accident during
transportation. The ham, however, was still suitable for human consumption. The
technician wanted to know whether the standard canning process was still
sufficient. He provided you with the information from the quality control
laboratory as described below. What would be your decision?

Approximate densities of microbial flora
in the ham before canning

Acceptable cell density in canned ham

Regular lot

Contaminated lot

Spoilage bacteria

IOO/ml

105/ml

0.00000001/ml and
fewer

Bacterial
spores

10/ml

104/ml

0.00000001/ml and
fewer

Fungal
spores

l/ml

10/ml

0.000001/ml and
fewer

Standard canning process for the
ham: 25 minutes at 105 0 C.

D values
and Z values

Spoilage
bacteria

Bacterial
spores

Fungal spores

of the microbes :

D value at 105 0 C

0.25
minute

2.5 minutes

0.5 minute

Z
value

7.50C

150C

150C

Answer the following questions. Show your calculations for
partial marks:

a.What
are the numbers of D'S targeted in the standard canning process for each
of these microorganisms? (3 marks)

You should understand the physico-chemical parameters that affect microbial growth and survival.

Temperature preferences and effects of different micororganisms.

The heat treatment in particular is an important way of food safety assurance and need to know all aspects on D value, Z value, and F value. You need to know how they are calculated and used in heat treatment scenarios.

Moisture contents vs water activities.

Strong acids and weak acids effects on growth and survival of different kinds of microorganisms.

Aerobic vs anaerobic respiration vs fermentation

Redox potential as a predictor of kinds of microorganism that grow on the food

How the phsico-chemical parameters are manipulated for prevention of foodborne diseases and food safety

●According to Chart I, what are the Z
values ofthe
two types of microbes? (4 marks)

Spoilage Bacteria: -(95-85)/ log 5- log 50=10°C

Bacteria Spores: -(105-90)/ log 5 - log 50 =15°C

●The canning temperature can be raised
15°C without any adverse effect on the quality of the canned hams. Hence, the
technician would like to use l20°C in the canning process to treat this lot of
contaminated ham. Calculate the treatment time required at120°C to achieve (i)
the acceptable cell density for this contaminated lot and (ii) the acceptable
cell densities of the microorganisms of the regular lot of ham after canning
with this new process. Justify your answer and explain. (10 marks)

At 120°C:

Spoilage
bacteria:

D120°C=D105°C *10^[(105-120)/10]=0.25*10^(-1.5)=7.9*10^(-3)min

Bacteria Spores:

D120°C=D105°C
*10^[(105-120)/15]=0.25*10^(-1)=0.25min

Treatment time for regular:

Spoilage
bacteria: 10D120°C=7.9*10^(-2)min

Bacteria Spores: 9D120°C=2.25min

Treatment time for contaminated:

Spoilage bacteria: 13D120°C=0.1027min

Bacteria Spores: 12D120°C=3min

Your answers to the questions are correct except one: Your answer to the last question is incomplete: you can only use one treatment time to treat each lot. You need to use the time for the most heat-resistant microorganism, in this case, bacterial spores. So the times should be:

Message from Professor Kwan

--This blog provides resources for the Food Microbiology part of the course FNSC5110 .--Check this blog often to see what is new.--Lecture notes and powerpoints are listed in CUHK eLearning System.--Click the Glossary button to search information on food microbiology terms.